Field of the Invention
This invention relates generally to capacitance sensitive touchpads. More specifically, the present invention relates to the ability to configure a touchpad or touchpad detection circuitry such that insertion of any foreign conductive or dielectric material in a touch or proximity sensitive sensor area of the capacitance sensitive touchpad sensors will be detectable, wherein the foreign conductive or dielectric material is any object intended to intercept signals or detect objects that are generating signals, such as the capacitance sensitive touchpad, other circuits and switches.
Description of Related Art
There are several designs for capacitance sensitive touchpads. One of the existing touchpad designs that can be modified to work with the present invention is a touchpad made by CIRQUE® Corporation. Accordingly, it is useful to examine the underlying technology to better understand how any capacitance sensitive touchpad can be modified to work with the present invention.
The CIRQUE® Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated as a block diagram in FIG. 1. In this touchpad 10, a grid of X (12) and Y (14) electrodes and a sense electrode 16 is used to define the touch-sensitive area 18 of the touchpad. Typically, the touchpad 10 is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these X (12) and Y (14) (or row and column) electrodes is a single sense electrode 16. All position measurements are made through the sense electrode 16.
The CIRQUE® Corporation touchpad 10 measures an imbalance in electrical charge on the sense line 16. When no pointing object is on or in proximity to the touchpad 10, the touchpad circuitry 20 is in a balanced state, and there is no charge imbalance on the sense line 16. When a pointing object creates imbalance because of capacitive coupling when the object approaches or touches a touch surface (the sensing area 18 of the touchpad 10), a change in capacitance occurs on the electrodes 12, 14. What is measured is the change in capacitance, but not the absolute capacitance value on the electrodes 12, 14. The touchpad 10 determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line 16 to reestablish or regain balance of charge on the sense line.
The system above is utilized to determine the position of a finger on or in proximity to a touchpad 10 as follows. This example describes row electrodes 12, and is repeated in the same manner for the column electrodes 14. The values obtained from the row and column electrode measurements determine an intersection which is the centroid of the pointing object on or in proximity to the touchpad 10.
In the first step, a first set of row electrodes 12 are driven with a first signal from P, N generator 22, and a different but adjacent second set of row electrodes are driven with a second signal from the P, N generator. The touchpad circuitry 20 obtains a value from the sense line 16 using a mutual capacitance measuring device 26 that indicates which row electrode is closest to the pointing object. However, the touchpad circuitry 20 under the control of some microcontroller 28 cannot yet determine on which side of the row electrode the pointing object is located, nor can the touchpad circuitry 20 determine just how far the pointing object is located away from the electrode. Thus, the system shifts by one electrode the group of electrodes 12 to be driven. In other words, the electrode on one side of the group is added, while the electrode on the opposite side of the group is no longer driven. The new group is then driven by the P, N generator 22 and a second measurement of the sense line 16 is taken.
From these two measurements, it is possible to determine on which side of the row electrode the pointing object is located, and how far away. Pointing object position determination is then performed by using an equation that compares the magnitude of the two signals measured.
The sensitivity or resolution of the CIRQUE® Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of 960 counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes 12, 14 on the same rows and columns, and other factors that are not material to the present invention.
The process above is repeated for the Y or column electrodes 14 using a P, N generator 24
Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes 12, 14 and a separate and single sense electrode 16, the sense electrode can actually be the X or Y electrodes 12, 14 by using multiplexing. Either design will enable the present invention to function.
With this understanding of one capacitance sensitive touchpad, it is now possible to discuss the present invention and a particular application because of shortcomings in state of the art designs.
A problem that has arisen in point-of-sale (POS) devices is that they are vulnerable to tampering. The stealing of credit card information is on the rise and is a substantial cause of concern among consumers. Accordingly, there is a substantial benefit from making devices more secure that read confidential data from credit and debit cards that can be used to access accounts.
For example, there are many electronic devices that are used to read data stored on credit or debit cards. Most of these devices read information from a magnetic strip. However, other electronic devices read information from newer smart cards using radio frequency signals. Both of these types of electronic devices then enable a user to input a secret Personal Identification Number (PIN) in order to complete a transaction. The PIN is typically entered on a PIN Entry Device (PED). Vulnerabilities in the design of PEDs show that these vulnerabilities can be exploited using unsophisticated techniques to expose PINs, credit and debit card numbers and other cardholder data.
One method of obtaining PIN information is to detect PIN data as it is being entered from a keypad on the PED. Accordingly, it would be an advantage over the state of the art to provide a PED that would be able to detect the presence of a foreign object, such as a sensor designed to detect input without interfering with the process of providing input to the PED, wherein the input is typically confidential information. It would also be an advantage over the prior art to adapt the new means of detection of an intruding sensor to any device that can be tampered with in order to insert a sensor or other device that can monitor activity on the device.